Liquid crystal display, as a kind of common electronic equipment, has been widely used in people's daily life. In practical use, a Organic Light Emitting Display (OLED) is widely used because of its advantages such as low cost of production, self-luminous and no need of backlight, etc. During the preparation of the OLED, a mask plate is used to vapor-deposit luminescent material in the area of light-emitting pixels on a glass substrate. With the development of OLED technology, the size of the OLED display and the size of the glass substrate are constantly increasing, which also requires a continuous increase in the size of the mask plate, in order to ensure the accuracy of making the mask plate, the mask plate used in vapor-deposition is mostly used in the form of strip-shaped sub-mask plates. In general, when the strip-shaped sub-mask plate is welded on a bottom frame, the welding position is likely to occur position deviation, thereby resulting in the poor color mixing of prepared OLEDs, and further resulting in the production of defective products.